First, I like concept. Having a flexible online project planning tool that would allow me to see what needs to be done and export to something like Microsoft Project is great. What you have done right now looks very similar to a work breakdown schedule, but one thing it could use would be to set dependency. For example, it would be nice to be able to say that Item B can only be completed once Item A is completed. That way I could better determine the length of the project and where there is slack time.

Dependencies is a common request and we have thought long and hard about whether we should implement it or not. For now, dependencies is not on the roadmap, "Yap" is at the moment really focused on trying to achieve quick and easy planning. But we might be wrong, Check out the Lynx test drive on Projectplace Labs, there you will see an application with more deep functionality, it supports all kinds of dependencies, critical path etc.

And for the comment above about colors this is definitely something we will implement at some point.